Image reading devices, for example, a scanner, a copy machine, a printer, a facsimile machine, or other image reading devices, can receive a document having content (for example, images, text, combinations of them) and electronically process the content. For example, the copy machine can copy the content onto a sheet of paper. The scanner can convert the content into electronic format. Sometimes, it is desirable to electronically process content from multiple such documents. Sheet output stackers can receive multiple such documents. To do so, the image reading device and the sheet output stacker need to be mechanically and electrically coupled.